New install filter and pref-src action

The purpose of the this new filter is to override *locally*:
- RTA_SRC ('from' option in ip-route)
- RTA_PREFSRC ('src' in ip-route)

We also force use of ipv6 subtrees because:
- even Linux 2.6.32 has them
- the fallback implementation using a separate table is not equivalent,
  at least not for Nexedi (and we don't need RTA_SRC for ipv4)

TODO: documentation

To be pushed upstream.

babeld.h

@@ -80,11 +80,7 @@ THE SOFTWARE.
 #endif
 #endif
 
-#ifdef IPV6_SUBTREES
 #define has_ipv6_subtrees 1
-#else
-#define has_ipv6_subtrees 0
-#endif
 
 extern struct timeval now;
 extern int debug;

configuration.c

@@ -42,6 +42,7 @@ THE SOFTWARE.
 struct filter *input_filters = NULL;
 struct filter *output_filters = NULL;
 struct filter *redistribute_filters = NULL;
+struct filter *install_filters = NULL;
 struct interface_conf *default_interface_conf = NULL;
 struct interface_conf *interface_confs = NULL;
 
@@ -403,6 +404,15 @@ parse_filter(int c, gnc_t gnc, void *closure, struct filter **filter_return)
                 goto error;
             if(af == AF_INET && filter->action.src_plen == 96)
                 memset(&filter->action.src_prefix, 0, 16);
+        } else if(strcmp(token, "pref-src") == 0) {
+            int af;
+            c = getip(c, &filter->action.pref_src, &af, gnc, closure);
+            if(c < -1)
+                goto error;
+            if(filter->af == AF_UNSPEC)
+                filter->af = af;
+            else if(filter->af != af)
+                goto error;
         } else {
             goto error;
         }
@@ -832,6 +842,12 @@ parse_config(gnc_t gnc, void *closure)
             if(c < -1)
                 return -1;
             add_filter(filter, &redistribute_filters);
+        } else if(strcmp(token, "install") == 0) {
+            struct filter *filter;
+            c = parse_filter(c, gnc, closure, &filter);
+            if(c < -1)
+                return -1;
+            add_filter(filter, &install_filters);
         } else if(strcmp(token, "interface") == 0) {
             struct interface_conf *if_conf;
             c = parse_ifconf(c, gnc, closure, &if_conf);
@@ -1064,6 +1080,19 @@ redistribute_filter(const unsigned char *prefix, unsigned short plen,
     return res;
 }
 
+int
+install_filter(const unsigned char *prefix, unsigned short plen,
+               const unsigned char *src_prefix, unsigned short src_plen,
+               struct filter_result *result)
+{
+    int res;
+    res = do_filter(install_filters, NULL, prefix, plen,
+                    src_prefix, src_plen, NULL, 0, 0, result);
+    if(res < 0)
+        res = INFINITY;
+    return res;
+}
+
 int
 finalise_config()
 {

configuration.h

@@ -24,6 +24,7 @@ struct filter_result {
     unsigned int add_metric; /* allow = 0, deny = INF, metric = <0..INF> */
     unsigned char *src_prefix;
     unsigned char src_plen;
+    unsigned char *pref_src;
 };
 
 struct filter {
@@ -61,4 +62,7 @@ int redistribute_filter(const unsigned char *prefix, unsigned short plen,
                     const unsigned char *src_prefix, unsigned short src_plen,
                     unsigned int ifindex, int proto,
                     struct filter_result *result);
+int install_filter(const unsigned char *prefix, unsigned short plen,
+                   const unsigned char *src_prefix, unsigned short src_plen,
+                   struct filter_result *result);
 int finalise_config(void);

disambiguation.c

@@ -34,6 +34,7 @@ THE SOFTWARE.
 #include "route.h"
 #include "source.h"
 #include "neighbour.h"
+#include "configuration.h"
 
 struct zone {
     const unsigned char *dst_prefix;
@@ -207,32 +208,51 @@ is_installed(struct zone *zone)
                              zone->src_prefix, zone->src_plen) != NULL;
 }
 
+static const unsigned char *install_zone(struct zone *zone)
+{
+    struct filter_result filter_result;
+
+    if(INFINITY == install_filter(zone->dst_prefix, zone->dst_plen,
+                                  zone->src_prefix, zone->src_plen,
+                                  &filter_result))
+      return NULL;
+
+    if(filter_result.src_prefix) {
+      zone->src_prefix = filter_result.src_prefix;
+      zone->src_plen = filter_result.src_plen;
+    }
+    return filter_result.pref_src;
+}
+
 static int
-add_route(const struct zone *zone, const struct babel_route *route)
+add_route(struct zone *zone, const struct babel_route *route)
 {
+    const unsigned char *pref_src = install_zone(zone);
     return kernel_route(ROUTE_ADD, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop,
                         route->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0);
 }
 
 static int
-del_route(const struct zone *zone, const struct babel_route *route)
+del_route(struct zone *zone, const struct babel_route *route)
 {
+    const unsigned char *pref_src = install_zone(zone);
     return kernel_route(ROUTE_FLUSH, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop,
                         route->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(route)), NULL, 0, 0);
 }
 
 static int
-chg_route(const struct zone *zone, const struct babel_route *old,
+chg_route(struct zone *zone, const struct babel_route *old,
           const struct babel_route *new)
 {
+    const unsigned char *pref_src = install_zone(zone);
     return kernel_route(ROUTE_MODIFY, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         old->nexthop, old->neigh->ifp->ifindex,
                         metric_to_kernel(route_metric(old)),
                         new->nexthop, new->neigh->ifp->ifindex,
@@ -240,11 +260,12 @@ chg_route(const struct zone *zone, const struct babel_route *old,
 }
 
 static int
-chg_route_metric(const struct zone *zone, const struct babel_route *route,
+chg_route_metric(struct zone *zone, const struct babel_route *route,
                  int old_metric, int new_metric)
 {
+    const unsigned char *pref_src = install_zone(zone);
     return kernel_route(ROUTE_MODIFY, zone->dst_prefix, zone->dst_plen,
-                        zone->src_prefix, zone->src_plen,
+                        zone->src_prefix, zone->src_plen, pref_src,
                         route->nexthop, route->neigh->ifp->ifindex,
                         old_metric,
                         route->nexthop, route->neigh->ifp->ifindex,

kernel.h

@@ -67,6 +67,7 @@ int kernel_interface_wireless(const char *ifname, int ifindex);
 int kernel_interface_channel(const char *ifname, int ifindex);
 int kernel_route(int operation, const unsigned char *dest, unsigned short plen,
                  const unsigned char *src, unsigned short src_plen,
+                 const unsigned char *pref_src,
                  const unsigned char *gate, int ifindex, unsigned int metric,
                  const unsigned char *newgate, int newifindex,
                  unsigned int newmetric);

kernel_netlink.c

@@ -921,6 +921,7 @@ kernel_interface_channel(const char *ifname, int ifindex)
 int
 kernel_route(int operation, const unsigned char *dest, unsigned short plen,
              const unsigned char *src, unsigned short src_plen,
+             const unsigned char *pref_src,
              const unsigned char *gate, int ifindex, unsigned int metric,
              const unsigned char *newgate, int newifindex,
              unsigned int newmetric)
@@ -974,11 +975,11 @@ kernel_route(int operation, const unsigned char *dest, unsigned short plen,
            stick with the naive approach, and hope that the window is
            small enough to be negligible. */
         kernel_route(ROUTE_FLUSH, dest, plen,
-                     src, src_plen,
+                     src, src_plen, pref_src,
                      gate, ifindex, metric,
                      NULL, 0, 0);
         rc = kernel_route(ROUTE_ADD, dest, plen,
-                          src, src_plen,
+                          src, src_plen, pref_src,
                           newgate, newifindex, newmetric,
                           NULL, 0, 0);
         if(rc < 0) {
@@ -1070,17 +1071,24 @@ kernel_route(int operation, const unsigned char *dest, unsigned short plen,
         rta->rta_type = RTA_OIF;
         *(int*)RTA_DATA(rta) = ifindex;
 
-        if(ipv4) {
-            rta = RTA_NEXT(rta, len);
-            rta->rta_len = RTA_LENGTH(sizeof(struct in_addr));
-            rta->rta_type = RTA_GATEWAY;
-            memcpy(RTA_DATA(rta), gate + 12, sizeof(struct in_addr));
-        } else {
-            rta = RTA_NEXT(rta, len);
-            rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr));
-            rta->rta_type = RTA_GATEWAY;
-            memcpy(RTA_DATA(rta), gate, sizeof(struct in6_addr));
-        }
+#define ADD_IPARG(type, addr) \
+        do if(ipv4) { \
+            rta = RTA_NEXT(rta, len); \
+            rta->rta_len = RTA_LENGTH(sizeof(struct in_addr)); \
+            rta->rta_type = type; \
+            memcpy(RTA_DATA(rta), addr + 12, sizeof(struct in_addr)); \
+        } else { \
+            rta = RTA_NEXT(rta, len); \
+            rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr)); \
+            rta->rta_type = type; \
+            memcpy(RTA_DATA(rta), addr, sizeof(struct in6_addr)); \
+        } while (0)
+
+        ADD_IPARG(RTA_GATEWAY, gate);
+        if(pref_src)
+            ADD_IPARG(RTA_PREFSRC, pref_src);
+
+#undef ADD_IPARG
     } else {
         *(int*)RTA_DATA(rta) = -1;
     }

kernel_socket.c

@@ -385,6 +385,7 @@ kernel_interface_channel(const char *ifname, int ifindex)
 int
 kernel_route(int operation, const unsigned char *dest, unsigned short plen,
              const unsigned char *src, unsigned short src_plen,
+             const unsigned char *pref_src,
              const unsigned char *gate, int ifindex, unsigned int metric,
              const unsigned char *newgate, int newifindex,
              unsigned int newmetric)
@@ -401,8 +402,9 @@ kernel_route(int operation, const unsigned char *dest, unsigned short plen,
         {{{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
             0x00, 0x00, 0x00, 0x00, 0x7f, 0x00, 0x00, 0x01 }}};
 
-    /* Source-specific routes are not implemented yet for BSD. */
-    if(src_plen > 0) {
+    /* Source-specific routes & preferred source IPs
+     * are not implemented yet for BSD. */
+    if(src_plen > 0 || pref_src) {
         errno = ENOSYS;
         return -1;
     }